Coating composition



United States Patent O ice COATING COMPOSITION John R. Gimler,Morristown, N. J.

No Drawing. Application December 1, 1953, Serial No. 395,607

2 Claims. (Cl. 106-468) This invention relates to c'oatingcompounds,more particularly compositions for coating and sealing cartons orpackages of goods which must be protected from the damaging effects ofthe weather, more particularly the effects of moisture and humid airwhich may corrode or otherwise damage the goods.

For example, in the case of a large number of products required formilitary uses, it is necessary that the goods be packaged for transportto the point of use in a suitable container or wrapping and that thelatter be enveloped with an applied coating or sealing compound intendedto prevent the ingress of moisture or humid air through the container orwrapping to an extent such as which would enable it to come into contactwith and deleteriously affect the goods.

With that in view, the container or wrapped package of the goods iscustomarily provided with a seal coating applied thereto in the form ofa molten thermoplastic composition, the container or package beingcompletely immersed therein so as to provide a coating film or layer ofdesired thickness over the entire surface thereof.

Having in view the requirements that must be met by the coating film,from the standpoint of its application to the package, the atmosphericand other conditions which are encountered before the packaged item isremoved and put to its intended use, the compositions heretoforeemployed for this purpose, and more particularly those which conform tothe requirements of certain Federal specifications for such products,have consisted of certain petroleum waxes, more particularly a so-calledmicrocrystalline wax. Microcrystalline waxes are well known and haveheretofore also been widely used, in combination with certain additives,as adhesive for uniting plies of paper or the like and as moisture-proofcoatings upon paper, cardboard, or the like.

These microcrystalline waxes are, generally speaking, amorphous,substantially saturated compounds formed from high-boiling-point,non-saturated petroleum derivatives by polmerization or condensation.When combined with certain additives, they may be rendered resistant tomoisture penetration and sufficiently adherent to serve as a bondbetween fibrous sheets. They'may be distinguished from the usualsaturated hydrocarbons known as parafiine, by their relatively highermelting-point.

The microcrystalline Waxes heretofore employed as dip coatings forcontainers or wrapped packages of goods have melting points of about 130F.

When used as a dip coating compound for the purposes above-mentioned, itis required, particularly in order to conform to certain Federalspecifications for such coat ings, that they exhibit the followingphysical character istics:

1. That they show no brittleness sufiicient to cause failure of thecoating-when in the form of a film of a thickness as much as A andsubjected for considerable periods of time to temperatures below minus20.". F., and in some casesaslow as minus 65 F 2. That the applied filmof the coating exhibit no flow- Patented June 25, 1957 ingcharacteristics or excessive tackiness when subjected to temperatures ofthe order of F. to F.;

3. Adequate tensile strength of the coating film;

4. Adequate resistance to abrasion of the coating film;

5. Adequate low moisture vapor transmission properties;

6. An increase not exceeding one percent in weight when immersed inwater for one week;

7. A penetration (standard needle, 5 seconds, 100 grams) of not morethan 60 nor less than 30.

The microcrystalline wax compositions heretofore employed as protectivecoatings for military packages, for example packages of rations,replacement parts, medical supplies, ammunition, and numerous otheritems, while satisfactory for protection of the packaged goods destinedfor use under climatic conditions encountered in the Warmer theaters ofoperation, have been found to be totally unsatisfactory when subjectedto conditions encountered in areas having much colder climate, suchas isthe case for example in Korea.

It has been found that under the latter conditions, the microcrystallinewax compositions employed prior to my invention as dip coating ofpackages of military goods or the like failed of their purpose in thatthey exhibit internal cracking or crazing whenencountering temperaturesof the order of minus 20 -F., or lower. Apparently this cracking orcrazing results from internal strains due to contraction of the filmwhen subjected to such cold shock.

Attempts made to rectify this inadequate resistance to cold shock on thepart of microcrystalline wax, by modifying the same with substancesdesigned to function as plasticizers, such as naphthenic petroleum oilshave shown that while improving the low temperature shock resistance ofthe composition these modifiers do not eliminate thetendency of thecompound to suffer internal crazing when exposed to temperaturessubstantially below minus 20 F. and furthermore serve to reduce themelting point of the compound below the required minimum.

Efforts made to remedy both these drawbacks in such mixtures ofmicrocrystalline wax and plasticizer by in-' corporating therein variousmetallic stearates, such as those of lead, calcium, barium, lithium andaluminum, have failed to give the desired results. Among otherobjections, the stearates of calcium, lithium, barium-and the highermelting-point stearates of aluminum can be uniformly incorporated in thecompound only with great ditficulty and, moreover, these additives arefound to crystallize out of the compound at the normal dip coatingtemperatures. The stearates of lead, as well as the low melting pointstearates of aluminum, are incapable of imparting to the compound thenecessary resistance to low emperature crazing, are only moderatelyeffective in raising the melting-point of the plasticizedmicrocrystalline wax, and'in the case of the aluminum stearates, causeundesirable foaming when incorporated in the molten wax.-

The principal object of the present invention is to provide acomposition suitable for use as a coating to be applied to containersor'packages. of' goods, more particularly goods used by the. military,and which such coating is capable of being applied as acontinuous'film-on such containers or packages 'by immersion'thereof ina bath of the molten compound, the compound'possessing properties whichwill satisfy the several requirements above enumerated.

A further object of the invention is to provide a compo-; sition of thecharacter indicated, which may be compounded and shipped in bulk forapplication at the point wherethe goods to be protected thereby arepackaged or wrapped for shipment.

Still another object is to provide a-dip coating composition of the'character indicated, which whe'n utilize'ii as and for the purposesaforesaid will serve elfectively to prevent damage to or deteriorationof the packaged or wrapped item by ingress of moisture or moisture-ladenatmosphere or by escape of moisture from the packaged product, as in thecase of food or the like.

Theseand other-objects of the invention, and the advantages thereof,will be readily apparent to those skilled in the 'art from the moredetailed description below. j According to the invention, the coatingcomposition comprises a mixture of microcrystalline wax, a plasticizerfor-the wax, more particularly a naphthenic oil'derivative of petroleumof relatively low pour point, and a substance functioning to impart tothe composition substantially complete resistance to internal crazing attemperatures, substantially below minus 20 F., and at the same time toprovide a composition having a softening point higher than 150 F.

More particularly, according to the invention, this last namedingredient of the composition is the zinc soap of stearic acid. Ihavefound that when employed in a proportion of from about 0.75 to 1.5percent by weight of the composition, the resultant product possessesthe properties indicated and fully meets the rather severe requirementsof the military, as exemplified by the physical characteristics aboveenumerated.

In the composition made according to the invention, the naphthenic oilplasticizer is employed in an amount of about five to ten percent byweight of the wax.

Example I Minimum Maximum Ideal Mlerom'ystalllne Wax Plastlcizer Zincstearate In the above formulation, the plasticizer used was a naphthenicoil having a pour point of minus 60 F., obtainable from Socony VacuumOil Company under its trade designation Solvaloid L. The zinc stearatewas a technical grade obtainable on the open market. Themicrocrystalline wax was a material obtainable from Socony Vacuum.0ilCompany under its trade designation S/V-2305, and had a melting-point of155 F. min. (ASTM).

In compounding the composition, the molten microcrystalline wax may bepumped into a jacketed, steamheated mixing tank provided with a paddleor so-called lightning type agitator, and while subjecting the wax toslow speed agitation therein, the plasticizer and the zinc stearate maybe added. Since the zinc stearate melts at approximately 257 F., it isnot necessary, or advisable, to permit the temperature of the batch toexceed the range of 275 to 300 F. When the batch is completelyhomogeneous, it may be screened to remove any extraneous foreign matterand then pumped to a tank car for shipment or packaged as required.

Alternatively, in making this composition, a masterbatch oftheplasticizer and the zinc stearate may be formed under moderate agitationin a suitable tank or churn, and when completely homogeneous, themasterbatch may be pumped at the required rate to the steamheated mixingtank containing the melted wax. In this procedure, as in the one firstmentioned, the temperature in the mixing tank must be above 260 F.'inorder properly to incorporate the zinc stearate, but it is neithernecessary nor advisable that the temperature therein exceed 300 F. Whenthe mixture is homogeneous, that is to say, free from specks of zincstearate, it may be run through a screen and either pumped to a tank caror packaged as required, for shipment.

The compound illustrated in this example had a softening point ofapproximately 153 F., and a penetration of approximately 41 (standardneedle, grams, 5 seconds). When tested under ASTM test method D98848T(73 F. at 50% relative humidity) this product showed zero moisture vaportransmission during a 168 hour test. As to homogenity, it showed noseparation and no residue when heated at 210 F. for 72 hours.

Samples of the product cast in molds so as to have a cross-section ofone by two centimeters and pulled in a Scott tensile testing machine atthe rate of 2.5 inches per minute showed an average tensile strength ofapproximately 14 pounds per square inch.

The time required for a coating film of & inch thickness to setcompletely was between 45 and 50 seconds. When tested by immersion inwater for one week according to the water-absorption test set forth inthe applicable Federal Specification, its water absorption was nil.

A test package containing a solid object, wrapped in scrim clothlaminated to a layer of polyethylene conforming to applicable FederalSpecification for such wraps, and then coated by dipping twice in themolten compound of this example, showed no flaking or cracking of thecoating after three weeks exposure to a temperature of 65 below zeroFahrenheit. The compound showed no discontinuities in congealing fromits liquid to the solid state.

Even a inch thick film of the composition passed the standard /z'mandrel test at that low temperature.

In referring to the resistance of the coating film to cracking whensubjected to those low temperatures, it should be borne in mind thatthis means its resistance when applied to the surface of a solid object,for if the object to which it is applied is of a character orconformation such as itself to undergo contraction or similardistortion, these latter influences may cause the coating to crack.Thus, for example, if the coating composition of my invention is appliedto the surface of a partially-filled container or to the surface of awrapping which consists of material such as scrim cloth laminated tocellophane or the like, the flexibility of the container in the onecase, or the cellophane in the other case, may itself cause it toundergo such distortion as thereby to cause the film of the coatingcomposition to crack, whereas this would not occur if the coatingmaterial of the invention is applied, as intended, to a relatively firm,rigid surface which itself does not undergo shrinkage or similardistortion when subjected to such low temperatures.

Example II Although the product made according to Example I above setforth possesses, among its other desirable physical characteristics, theability to withstand the effects of cold shock to the extent of completeresistance to internal cracking or crazing when subjected totemperatures well below minus 20 F., its softening point ofapproximately 153 F. does not provide suflicient heat stability toenable it to resist flowing or so-called run-off at temperatures aboveF., say at a temperature of F. In certain instances it is necessary thatthe compound, in addition to resistance to such cold shock shall possessalso the ability to withstand run-off at a temperature of approximately165 F.

This latter property is provided in the embodiment of the inventionrepresented by the present example. According to this example, there isincluded in the composition a substantial proportion of amicrocrystalline wax having a melting point of approximately F., alongwith the microcrystalline wax included in Example I, viz., the onedesignated S/V2305. For best results, the 180 F. melting-pointmicrocrystalline wax is employed in a ratio of approximately one partthereof with 8 to 10 parts of the S/V2305 microcrystalline wax, byweight. Furthermore, as will be noted from the figures given below, thenaphthenic hydrocarbon plasficizer is employed in an amount ofapproximately based on the combined weight of both microcrystallinewaxes present in the compound, in contrast to approximately 6% by weightg of plasticizer in relation to the microcrystalline wax pres-Microcrystalline wax (180 F. melting-point) 10.0 Pl asticizer (as inExample I) 8.0 Zinc steal-ate- 1.0

This product has a specific gravity of 0.8375 and Weighs 6.98 pounds pergallon. Tested as hereinabove set forth, it exhibited no cracking orflaking at a temperature of minus 20 F. and no run ofi. at 160 F.Likewise, it met by a considerable margin the other requirements as tophysical properties enumerated above for use as a dip coating compoundfor protecting packages or containers of the class to which referencehas been made.

The term consisting essentially of as used in the claims to define theingredients present in the claimed composition is intended to excludethe presence of other materials in such amounts as to interferesubstantially with the properties and characteristics possessed by thecomposition set forth, but to permit the presence of other materials insuch amounts as do not substantially affect said properties andcharacteristics adversely.

Having described my invention, what I claim is:

1. A coating composition characterized by substantially completeresistance to internal cracking or crazing when in the form of anapplied film on a substantially rigid surface and subjected totemperatures of the order of minus F., and having a softening point notsubstantially below F., said composition consisting of approximately 93parts by weight of microcrystalline wax, approximately 6 parts by weightof a naphthenic petroleum oil having a pour point of minus 60 F., andapproximately 1% by weight of zinc stearate.

2. A coating composition characterized by substantially completeresistance to internal'cracking or crazing when in the form of anapplied film on a substantially rigid surface and subjected totemperatures substantially below minus 20 F., and exhibiting heatstability sufficient to prevent it from running ofl? a surface attemperatures of the order of F. to F., said composition consisting ofapproximately 81% of a microcrystalline Wax having a melting-point of155 F., approximately 10% of a microcrystalline wax having amelting-point of F., approximately 8% of a naphthenic petroleum oilhaving a pour point of minus 60 F, and approximately 1% of zincstearate, all by weight.

References Cited in the file of this patent UNITED STATES PATENTS2,099,880 Ellis Nov. 23, 1937 2,348,689 Abrams et al. May 9, 19442,375,348 Cohen May 8, 1945 2,464,759 Camp Mar. 15, 1949 2,546,328Arabrian et al Mar. 27, 1951 2,595,158 McCue et al. Apr. 29, 19522,641,551 Smith et al. June 9, 1953

1. A COATING COMPOSITION CHARACTERIZED BY SUBSTANTIALLY COMPLETERESISTANCE TO INTERNAL CRACKING OR CRAZING WHEN IN THE FORM OF ANAPPLIED FILM ON A SUBSTANTIALLY RIDIG SURFACE ANS SUBJECTED TOTEMPERATURES OF THE ORDER OF MINUS 60*F., AND HAVING A SOFTENING POINTNOT SUBSTANTIALLY BELOW 150*F., SAID COMPOSITION CONSISTING OFAPPROXIMATELY 93 PARTS BY WEIGHT OF MICROCRYSTALLINE WAX, APPROXIMATELY6 PARTS BY WEIGHT OF A NAPHTHENIC PETROLEUM OIL HAVING A POUR POINT OFMINUS 60*F., AND APPROXIMATELY 1% BY WEIGHT OF ZINC STEARATE.